Unit for viewing the restart of time-dependent fluid flow

ABSTRACT

The present invention refers to a unit for viewing the time-dependent fluid flow restart, comprising two hydraulically connected reservoir tanks ( 1, 2 ); two auxiliary pipes ( 3 ); a main pipe ( 4 ) between the reservoir tanks ( 1, 2 ) and between the auxiliary pipes ( 3 ); a viewing box ( 15 ); a pressurization system ( 20 ); data acquisition software; and a particle image velocimetry (PIV) system ( 8 ); wherein the main pipe ( 4 ) is made of a transparent acrylic material that allows the viewing of the fluid inside the same; wherein the viewing box ( 15 ) encompasses the main pipe ( 4 ) and allows its viewing; and wherein the unit views the restart of the time-dependent fluid flow in transient regime.

FIELD OF THE INVENTION

The present invention pertains to the technical field of oil production processes, more specifically, in the sector of lifting and flowing technologies.

The present invention describes a unit for studying technical information for the fluid flow process after interruptions in production or restarting the flow of gelled drilling fluids after shutdowns in the drilling process.

BACKGROUND OF THE INVENTION

The gelation of fluids is a problem of high relevance in several industrial sectors, particularly for the offshore industry of oil and paraffinic oils where materials with complex properties are transported through long pipelines.

In ultradeep water fields, the most common scenario in Brazil, extensive production lines positioned on the seabed imply important challenges with regard to flow assurance. Due to the length of the pipelines, the oil coming from the reservoirs at high temperatures is cooled, giving heat to the marine environment.

The reduction in temperature results in a decrease in the solubility of paraffin in oil. Below a certain temperature, called the crystallization temperature, paraffin crystals precipitate and settle on the internal walls of the oil pipelines.

The precipitation of crystals in the flow changes the behavior of the oil, which starts to behave like a suspension, evidenced by a significant increase in its viscosity.

In any production shutdowns, the suspended crystals in the oil can interconnect and gel the material in the pipelines, making it difficult or even preventing the restart of the flow, especially when these shutdowns are of long duration.

To resume the flow of gelled fluids, it is first necessary to break the gel structure, which requires a restart pressure higher than that of steady state operation. This minimum pressure for the restart of oil flow is correlated with the yield strength (TLE) of the material, that is, a critical stress value below which no flow occurs.

In flows involving pasty materials or suspensions, however, the fluence transition (rupture) is often associated with the wall slipping phenomenon, which makes the estimation of the initial pressure, or restart of the flow, even more complex.

In the case of gelled oil, wall slipping manifests itself in a range of shear forces (shear stress) of low magnitude, such that wall slipping and fluence transition are coupled and directly related to the velocity gradients that arise during the transient process of breaking down the gel structure. Accordingly, these factors that influence the magnitude of the flow restart pressure must be analyzed and well understood, because, when the pressure is overestimated, it can result in very robust oil pipeline projects, which could make them unfeasible.

Some ways to evaluate the beginning of the flow of gelled fluids in pipes have been conceived, and include from studies that evaluate the hydrodynamics of the flow using experimental units and descriptive methods, to studies that evaluate the use of additives that help to improve the fluidity of this type of fluid.

U.S. Pat. No. 3,502,103 owned by Shell Oil, from 1970 and already in the public domain, for example, presents a unit that uses a less dense liquid to form a lubricating layer between the pipe wall and the oil, to reduce friction losses when pumping mineral oil through the pipe. The gelled oil moves in the form of a cap (plug) through the center of the pipe and water (lubricating fluid) forms a layer between the oil and the wall of the pipe, facilitating the flow. This document made it possible to analyze the transport of very rigid hydrocarbons through pipelines.

U.S. Pat. No. 4,056,335 owned by United Steel Corporation and Patent EP 0322958 B1 owned by Shell Internacionale, both also in the public domain, in turn, describe experimental units to study the beginning of the flow of extremely viscous crude oils from offshore reservoirs. The experimental units were equipped with submersible pumps to simulate the field conditions. An important aspect of these two inventions is that water is injected and mixed with crude oil inside a cavity at the base of the submersible pump, thus decreasing the fluid effective viscosity and also controlling the pump operating temperature. The two units differ only in that the first uses a submersible pump driven by a conventional surface impeller and the second a submersible pump impeller.

U.S. Pat. No. 5,348,094 owned by the French Petroleum Institute, also in the public domain, presents an experimental unit and a method for flowing a high viscosity fluid containing a certain proportion of gas, wherein the pump is connected to the bottom end of a tubular string at the bottom of a well to move the fluid from this position to a production zone on the surface.

Patent BR 102016019029-0 owned by Petrobras discloses a system and a method of restarting flow in pipelines that allow the degradation of the gelled fluid without causing high pressure peaks in the pipe and without using chemical additives in the fluid. Said patent makes use of a system formed by at least one relief reservoir connected to the pipe, which receives the fluid flowing through the pipe. Several reservoirs may still exist along the pipe. The system also has a pressurizing element upstream of one of the reservoirs, adapted to pressurize the fluid in the pipe.

The patents listed below make use of different procedures for the flow of gelled fluids.

U.S. Pat. No. 3,791,395, owned by the Atlantic Richfield Company, already in the public domain, provides a method to restart the flow of a gelled oil in the pipeline, at a pressure with a value below the usual value. The described method comprises the cyclic application of pressure peaks in the blocked region of the pipeline. These pressure peaks cause the structure of the gelled oil to degrade by shear, reducing its resistance to flow, with each subsequent pressure pulse being applied before the oil regains its original resistance to flow. Such a process is carried out until the desired reduction in restart pressure is reached. This method allows a restart of flow with higher flow rates for the same inlet pressures, when compared to the flow rates obtained in cases where the pressure pulses are not used.

The U.S. Pat. No. 4,745,937, owned by the Venezuelan company Intevep, SA, already in the public domain, is related to a process to restart the flow in the form of a plug of highly viscous oils in a pipeline after a long interruption in the flow. The method comprises introducing a fluid with low viscosity, such as water, into the pipeline through a pump, gradually increasing the flow of such fluid, preferably in a linear fashion, until a desired stationary state condition is reached, as well as the velocity necessary to form an annular flow. From there, the flow of the gelled oil starts and is gradually increased by adjusting the speed of a motor connected to the pump that induces the flow, or even by adjusting a control valve in the pipeline. In addition, the method aims at reducing the pressure peak applied during the flow restart operation by introducing a surfactant to the low viscosity fluid.

Finally, U.S. Pat. No. 6,110,238, owned by Clariant GmbH, provides a method to improve the cold flow properties (pour point and plugging point) of fuel oils through the addition of additives, such as copolymers of lower olefins and vinyl esters, while preserving the filterability of the oils. Similarly, U.S. Pat. No. 3,048,479, owned by Exxon Research Engineering Co., already in the public domain, provides a method to improve the fluidity of oil-derived fuels, which have a specific boiling temperature range, through the introduction of an ethylene copolymer and a fatty acid vinyl ester.

With respect to the most current technologies, the Federal Technological University of Parana (UTFPR) developed an experimental apparatus described in the scientific paper entitled “Startup—Flow Viewing of Viscoplastic Fluid in horizontal pipes geometries using particle image velocimetry”, which discloses an experimental system to study the restart of the flow of viscoplastic fluids. As in the present invention, the paper also describes means for visualizing the flow restart through the particle image velocimetry (PIV) technique. However, the means used to carry out the flow of the fluid are different. In the paper, a pump is used so that the fluid leaves a tank, passes through an internal main pipe to a viewing box and returns to said tank, completing a cycle; meanwhile, in the present invention, means are used to pressurize the fluid in a tank so that the fluid flows towards a second tank, passing through an internal main pipe to a viewing box.

Accordingly, the present invention has a completely different configuration of imposition of external force (disturbance imposed on the fluid), that is, while the experimental apparatus of the UTFPR uses flow rate imposition by means of a hydraulic pump, the present invention uses a control system with high sensitivity and accuracy to control the pressure of compressed air, that is, pressure imposition. Therefore, by imposing flow rate, the fluid will flow no matter how small the flow rate is. The imposition of pressure gives the possibility of gradually imposing a force until the flow restarts.

Furthermore, the present invention works at much lower pressure ranges than those reported in the paper. These lower pressure values allow obtaining Reynolds numbers equal to or less than Re≤1, which from the point of view of flow dynamics provides a better understanding of the behavior of the fluid during flow restart (transient regime). The experimental apparatus reported by UTFPR only allows Re≥10, making it impossible to study the elastic effects and the gradual disruption of time-dependent fluids during flow restart, since this process is a phenomenon that occurs at low Reynolds.

The viewing section of the unit of the present invention is formed by a transparent acrylic box that is filled with water and a tubular section also made of acrylic, while the viewing section of the experimental apparatus developed by UTFPR is made of pure acrylic. This simple fact affects the index of refraction of light. Therefore, the quality of images displayed using the UFPR apparatus is inferior to those of the present invention.

The quick-closing valves located at the inlet and outlet of the test section of the present invention allow evaluating and analyzing the effects of compressibility in time-dependent fluids, closing them according to the operating configuration. The UTFPR experimental apparatus does not allow this study to be carried out because it does not have these accessories.

The test section of the present invention allows the analysis of the restart of the flow in pipelines with smooth and rough walls, thus evaluating the effects of hydrodynamic quantities such as the phenomenon of slipping on different surfaces, while the experimental apparatus of UTFPR does not allow to do this comparison.

U.S. Pat. No. 7,437,247, owned by the French Petroleum Institute, refers to a method to determine the conditions for resuming the flow of paraffinic oil considering output parameters such as pressure and thermal factors that influence the process. However, this document does not present any evidence that views and evaluates the process in a transitory way, that is, the disruption of the fluid core as a function of time. The present invention, in addition to presenting a method, proposes a unit that allows the viewing, analysis and evaluation of the restart of the flow, as well as the phenomena present in the process of disruption and time-dependent starting of fluids. The present invention further allows the rheological characterization of any time-dependent fluid using velocity profiles (the first derivative of velocity). This characterization method is more practical and requires fewer points compared to rheological tests.

As can be seen from the disclosure above, the patents and papers presented in the state of the art describe experimental units, apparatuses or systems that propose to use different devices that help in the study of the restart of flow of gelled fluids. Likewise, methods ranging from the implementation of transport processes to the use of chemical products that favor the starting of the flow are proposed.

However, the reported inventions do not provide relevant information for calculating the minimum pressure to break the gelled fluid and restart the flow, nor is it indicated how this pressure can be affected by the effects of the slipping phenomenon.

In addition, there is no evidence reported on viewing of the transient degradation process of gelled gel, and how it is possible to establish a relationship between slipping, shear forces and velocity gradients during this gel breakdown process (transient break).

Faced with all the problems glimpsed by the documents of the state of the art, the present invention sought to develop a unit whose main advantage refers to the reduction of the costs of new projects, particularly those related to the definition of the structure of the pipes, which are dimensioned to support pressures much higher than the real ones, due to the lack of knowledge of the conditions for restarting the flow. In addition, with the possibility of obtaining a flow curve obtained in the unit, the present invention proposes to obtain rheological parameters closer to those verified in daily operations, which may bring savings in operational terms. The possibility of visualizing the breakage of the gel and the knowledge of the breakage process bring advantages in the development of future devices and processes that facilitate (reduce the pressure) the restart of the flow. The knowledge of how the voids appear and form will also give subsidies for the evaluation of the real process of operation in cases of beginning of flow.

In addition, from the present invention, a better knowledge of the gel breaking process will also avoid a possible rupture of the pipeline when in operation, thus protecting the environment and avoiding costs of loss of production and costs related to recovery of the environment affected by any accident.

Thus, it is clear that the documents cited and commented above do not present similar studies or processes nor the possible technical advantages of the present invention, as reported above. Therefore, it is possible to note that the state of the art lacks a unit for the study of technical information for the fluid flow process after interruptions in production or restart of the flow of gelled drilling fluids after shutdowns in the drilling process, as detailed in follow.

SUMMARY OF THE INVENTION

The present invention has as the main objective providing a unit for calculating the pressure required to start/restart the flow of gelled fluids using the particle image velocimetry system (PIV System). Through the unit, the process of temporary breakdown of the gel structure can be analyzed as well as the phenomenon of wall slipping which is correlated with shear stress and velocity gradients in the wall.

Thus, in order to achieve this objective, the present invention proposes a unit for viewing the restart of time-dependent fluid flow comprising two hydraulically connected reservoir tanks, two auxiliary pipes, a main pipe between the reservoir tanks and between the pipes auxiliaries, a viewing box, a pressurization system, data acquisition software and a Particle Image Velocimetry (PIV) system, wherein the main pipe is made of a transparent acrylic material that allows the viewing of the fluid inside of the same, wherein the viewing box encompasses the main pipe and allows its viewing, and wherein the unit views the restart of the time-dependent fluid flow in transient regime.

BRIEF DESCRIPTION OF THE FIGURES

The detailed description presented below makes reference to the attached figures and their respective reference numbers, representing the embodiments of the present invention.

FIG. 1 shows an embodiment of the unit for viewing of the time-dependent fluid flow restart of the present invention.

FIG. 2 shows the unit for viewing of the time-dependent fluid flow restart of the present invention with the thermostatic bath.

FIG. 3 shows the enlarged pressurization system of the unit for viewing of the time-dependent fluid flow restart of the present invention.

DETAILED DESCRIPTION

The present invention describes a unit for displaying the time-dependent fluid flow restart represented by FIG. 1 in which two reservoir tanks are defined, a left one called LH (1) and a right one called RH (2), hydraulically connected, and two auxiliary pipes (3) made of PVC that connect the reservoir tanks (1) and (2) to the main pipe (4). FIG. 1 illustrates the unit configuration for displaying the time-dependent fluid flow restart system of the present invention.

The reservoir tanks (1, 2) have an adapter (16) on the top cover of each tank and that allows the entry of compressed air so that the fluid is pressurized and flows through the pipes from one tank to the other. In addition, the tanks contain a Bourdon-type pressure gauge (12), a pressure relief valve (11) and a sight gauge (9) installed on the side of each tank to visualize the fluid level inside the tanks (1, 2).

The main pipe (4) is made of polymethylmethacrylate (PMMA), an acrylic material that provides good mechanical strength to withstand the applied pressure and transparency so that the observation of the flow through the pipe is possible, and is located within a viewing box (15) made of acrylic. The main pipe (4) and the viewing box (15) are transparent and make up the test section to visualize the flow.

The pressurization system (20) responsible for providing the necessary pressure to restart the flow consists of the pressure regulator valve (10), the solenoid valves (14), the pressure gauges (12) and the pressure relief valves (11), wherein the first two are located upstream of the reservoir tanks (1) and (2) and the last two are installed on the top cover of each tank (1) and (2).

The pressure regulator valve (10) allows the control of the value of the pressure to be applied in the system through an interface with the data acquisition software. By means of this control, it is possible to monitor and apply constant and pre-defined pressure values that allow obtaining important information to evaluate the flow restart, such as velocity profiles.

In turn, the solenoid valves (14) define the tank to receive the compressed air used to pressurize the fluid, that is, when one tank is pressurized, the other is blocked and vice versa.

During the restart of the flow, the operating pressure is measured through pressure sensors (5) installed in the auxiliary pipe (3), externally to the viewing box (15), which connect the inlet and outlet of the main pipe (4).

The operating temperature of the restart of the flow is monitored through four thermocouples (7) fixed outside the main pipe (4) and internally to the viewing box (15), and two other thermocouples (7) fixed inside of each reservoir tank (1, 2). With thermocouples, it is possible to record the temperature at which the system is found during the flow restart tests, allowing the analysis of flow behavior and fluid properties for each temperature value at a given applied pressure.

To help control the temperature, a thermostatic bath (19) is installed near the unit and connected to the viewing box (15) through two thermally insulated hoses (17, 18) two meters long.

The temperature control system is shown in FIG. 2 and works as follows: through the inlet hose (inlet water) (17) water enters at a certain temperature (test temperature) and through the outlet hose (outlet water) (18) the water returns to the thermostatic bath (19) to be cooled again. This cycle is maintained for the entire duration of the test. This system is responsible for supplying and maintaining the test section at the desired temperature.

Two manual check/shutoff valves (6), made of PVC, are installed in the auxiliary pipes (3), wherein one is located before the flow inlet in the main pipe (4) and the other in the flow outlet from the main pipe (4). The state of each one (open or closed) depends on the flow restart test procedure used.

The present invention can be easily adapted to high pressures and a temperature range between 4° C. and 60° C., existing conditions in the production and drilling of offshore wells.

In order that the velocity profiles, the slipping velocity on the pipe wall and the fluid breakdown can be analyzed and evaluated, the unit makes use of the Particle Image Velocimetry System (PIV) (8). Such a system consists of smaller subsystems represented by the pulsed laser, the camera (which captures the flow image), a timer (responsible for synchronizing the laser emission with the camera to capture the image) and the image processing software (responsible for processing the captured image). In the present invention, the most suitable configuration has the angle between the pulsed laser and the camera set at 90°, in order to obtain images of the plane formed by the laser beam in the flow.

Once the images of the flow are obtained, the image processing and treatment software will allow the calculation of velocity profiles and gradients.

The yield stress is calculated directly from the velocity profiles through its first derivative (velocity gradients). According to the shape of a velocity profile, its first derivative, which also represents the real shear velocity for unidirectional flow, should become zero at the position where the shear stress reaches the fluence value. Then, the first derivative of velocity as a function of radial position (dv/dr) for the profile obtained for each Δp indicates the position where dv/dr=0, and which corresponds to a limiting shear stress value (Ty).

Finally, with the yield stress value (TLE), the minimum restart pressure is calculated using the equation (τ_(y)=ΔpD/4L).

Depending on the velocity profiles, it is possible to extrapolate the velocity value at r=R, that is, the value of slipping on the wall. Then, using a second-order polynomial fit (y=ax²+bx+c) at this position, it is possible to calculate the slipping velocity on the wall.

Next, with the values of shear stress and velocity gradients on the wall, it is possible to establish a relationship with the slipping velocity for each pressure drop value imposed as a function of time.

The transient breakdown of the gelled fluid is also established as a function of each pressure value and as a function of the time of application of this pressure, thus allowing the evaluation of the degradation of the gelled structure.

Example of Embodiment/Tests/Results

The specific experiments and tests that were carried out using the unit of the present invention directly involve the restart of the time-dependent fluid flow, through which it was possible to obtain data on wall shear stresses, wall velocity gradients, profiles of velocity and that in turn allowed to obtain more realistic data of values of the minimum pressure to be imposed to restart the flow. As an example of an experiment carried out to evaluate the transient response of fluids as a function of pressure drop (shear stress), experimental tests were carried out at a temperature of 22° C., following the protocol (step by step) described below:

-   -   1—Defining the required pressure;     -   2—Starting recording the pressure measurements 10 seconds before         imposing the pressure;     -   3—Beginning recording of pressure measurements and flow images         using the PIV technique ten seconds before opening the pressure         regulator valve;     -   4—Opening the pressure regulating valve;     -   Recording images at t=300 s using the PIV technique;     -   6—Recording images at t=600 s using the PIV technique;     -   7—Ending data recording at t=600 s;     -   8—Processing the pressure data and images obtained by the PIV         system;     -   9—Characterizing the fluid by calculating the yield stress (TLE)         using velocity profile data obtained using the PIV technique;     -   10—Comparing the flow restart data obtained in the rheological         tests with data obtained using flow restart viewing with the PIV         technique.

With the experimental procedure carried out in the unit, the yield stress (TLE) was obtained and then the pressure drop necessary to restart the flow of the stopped fluid (Δp_(exp)) was calculated. The Δp_(exp) results obtained through the unit data showed that the Δp reo calculated through the TLE of the rheological data was overestimated by more than 80%. The results were verified for three time-dependent fluids and in all three cases the TLE data obtained from the rheometric tests provided a much higher Δp reo than what was really necessary. In other words, while in the unit of the present invention the TLE obtained provided a smaller Δp_(exp) to restart the flow, the rheometric TLE data indicated that twice the value was needed (2×4p_(exp)).

In view of the results obtained, it can be concluded that the TLE obtained in the unit of the present invention allows calculating a much smaller Δp of flow restart than that calculated with rheometric tests, indicating that the Δp calculated through rheometric tests are overestimated in more than approximately 100%. An overestimation of the TLE may incur unnecessary expenses with equipment, diameters of fluid transport pipelines, and may even make the execution of large projects unfeasible due to the high operational cost.

Therefore, in view of the disclosure above and the experiments carried out, it is clear that the invention described herein provides a unit for the study of technical information and viewing of the process of restarting the flow of fluids, after interruptions or shutdowns in the drilling process, with more accurate data and closer to reality. In this way, the equipment used in the drilling can be better dimensioned. 

1. A system for displaying a restart of time-dependent fluid flow in a transient regime, a first reservoir tank containing a first fluid; a second reservoir tank containing a second fluid, wherein the first reservoir tank comprises a fluid and the second reservoir tank comprises another fluid; a first auxiliary pipe hydraulically connected to the first reservoir tank a second auxiliary pipe hydraulically connected to the second reservoir tank; a main pipe hydraulically connected to the first and second auxiliary pipes, wherein the main pipe is made of a transparent acrylic material that allows viewing of the fluid inside the main pipe; a viewing box surrounding at least a portion of the main pipe and allows its viewing; a pressurization system connected to the first and second reservoir tanks; and a particle image velocimetry (PIV) system positioned adjacent the viewing box to measure a fluid flow in the main pipe.
 2. The system of claim 1, wherein the first and second reservoir tanks are hydraulically connected to the main pipe through the auxiliary pipes.
 3. The system of claim 1, further comprising an adapter connected to a top cover of each of the first and second reservoir tanks, wherein the adapter allows the entry of compressed air to pressurize the first and second reservoir tanks and cause the first and second fluid to flow from one tank to another through the first and second auxiliary pipe and the main pipe; a sight gauge installed on a side of each of the first and second reservoir tanks to view a fluid level inside the tanks; and a thermocouple fixed inside each of the first and second reservoir tanks to record a temperature of the system during the flow restart tests.
 4. The system of claim 1, wherein the main pipe is made of polymethylmethacrylate (PMMA).
 5. The system of claim 3, wherein the pressurization system comprises: a pressure gauge connected to the top cover of each of the first and second reservoir tanks; a pressure relief valve connected to the top cover of each of the first and second reservoir tanks a solenoid valve fluidly connected to each adapter of each of the first and second reservoir tanks; and a pressure regulator valve fluidly connected to each solenoid valve of the first and second reservoir tanks.
 6. The system of claim 5, wherein the pressure regulator valve and the solenoid valves are located upstream of the first and second reservoir tanks.
 7. (canceled)
 8. The system of claim 6, wherein the solenoid valves allow the pressurization of only one reservoir tank and block the pressurization of the other tank reservoir tank.
 9. The system of claim 6, wherein the solenoid valves are installed downstream of the pressure regulator valve, and allow the air to flow both ways.
 10. The system of claim 1, wherein each of the first and second auxiliary pipes comprises a pressure sensors to measure an operating pressure and/or a pressure variation at the restart of the flow, wherein the measurements are used to determine a wall shear stress (τ_(w)) of the first and second auxiliary pipes.
 11. The system of claim 1, wherein each of the first and second auxiliary pipes further comprise a shut-off valve installed at an inlet and an outlet of the first and second auxiliary pipes, wherein the shut off valves control the fluid flow during the tests of fluid restart.
 12. The system of claim 1, wherein the main pipe further comprises four thermocouples, wherein the thermocouples are positioned outside and inside the viewing box and record a temperature of the flow restart.
 13. The system of claim 5, wherein the pressure relief valves installed on the cover of each reservoir tank are configured to depressurize the system.
 14. The system of claim 3, further comprising data acquisition software monitors and records the pressure and temperature values given by the pressure sensors and thermocouples.
 15. The system of claim 1, wherein the particle image velocimetry (PIV) system calculates a velocity profiles and velocity gradients, wherein a yield stress is calculated directly from the velocity profiles by means of their first derivative (velocity gradients).
 16. The system of claim 1, wherein the main pipe is immersed in water. 